1. Field of the Invention
The present invention relates to a developing apparatus and, more particularly, to an improvement over the developing apparatus of the type using a liquid developer with toner dispersed therein.
2. Description of the Prior Art
It is a common practice that an electrostatic latent image formed on the surface of a recording medium is processed in the developer including colored toners for the purpose of turning the latent image into a visible image. In such process, when the recording medium with electrostatic latent image on the surface is immersed in the developer, the electrostatic force causes the colored toners to be fixed on the surface of the recording medium, with the result that the latent image of electrostatic charges is colored to be visible. Such principle of development has widely been used in the electronic copying machine, and one form of such is disclosed in the U.S. Pat. No. 3,848,990, issued on Nov. 19, 1974, by Osamu Otsubo et al. In the copying machine of this type, the way to form the latent image on the recording medium is generally classified into two ways: One of them is that the recording medium per se is coated thereon with photoconductive material and the latent image is directly formed thereon; the other is that the latent image once formed on the sensitive means, such as a sensitive plate, is transferred onto the another surface, such as a sheet of paper. The developing apparatus is generally comprised of developer including colored toners, a developing trough where the development takes place, a tank for developer, and the like. In multicolor development, such developing apparatus is provided for each color used. When considering the development taking place in the just-mentioned developing apparatus, the electrostatic force of the charges of the latent image exerts on the paper in a narrow range as the recording medium passes through the developer. This range can be extended by increasing the amount of the electrostatic charges, and yet the effective electrostatic force can be at present heightened to be in the order of several hundreds micron at most. As a result, the colored tonors distanced from the recording medium beyond the region do not contribute to the development taking place in the developer, although the colored toners are included in the same developer. The amount of the colored toners existing in the region where there is only several hundreds micron is insufficient to obtain a satisfactory process of development. For this reason, in practical development work, an attempt has been made whereby the developer is constantly circulated by using a pumping means for refreshing the developer in the vicinity of the surface of the recording medium. However, the result of such attempt felt short of expectations. That is, the old developer residing close to the recording medium forms so-called boundary layers along the surfaces thereof due to the viscosity of the developer and thus only a small amount of old developer is exchanged in this vicinity, which results in the necessity for a long developing operation period for satisfactory quality of development.